Much is known about the regulation of gene expression underlying mammalian somatic cell growth and differentiation, but a similar understanding of these processes in generating haploid germ cells has been limited by the lack of appropriate cell cultures and because few genes have been analyzed that are expressed specifically in meiotic cells. Our work has now reached the stage where we have the essential reagents and background to investigate the genetic regulatory code for sperm cell differentiation, and perhaps also for oocyte development. Moreover, our studies of a gene product expressed specifically in meiotic cells, the enzyme lactate dehydrogenase C (LDH-C) have provided surprising evidence that the function of this protein in sperm maturation may go beyond the enzymatic to a structural role in the sperm and a regulatory role in mRNA translation. Our planned experiments will address three critical hypotheses in germ cell development: 1) Sperm cell-specific transcription factors are required for meiotic cell-specific gene expression. The LDH-C gene provides an ideal system in which to explore this question. 2) The LDH-C protein also will allow us to test the idea that this enzyme has important functions other than catalysis, including in cell structure and translational control. 3) We propose that what we find in the sperm will prove to be of general importance in meiotic cells, and thus for LDH-C both the cell-specific regulation of gene expression and the specific functions of the protein are predicted to be relevant to both sperm and oocytes. This proposal has three Specific Aims. Aim 1: To characterize the TF's required for testis specificity of Idhc expression. Aim 2: To study non-catalytic functions of LDH-C4. We will identify protein-protein interactions that tether LDH-C4 to the fibrous sheath and protein-nucleic acid interactions that may regulate testis gene translation. Aim 3: To measure Idhc expression in oocytes. The presence of LDH-C4 in the ovary may implicate it as a meiotic factor rather than a sex-specific germ cell factor and provides a target gene for studying molecular events in the oocyte. Completion of these specific aims will further our understanding of LDH-C4 function, of testis specific gene regulation and of macromolecular interactions necessary for normal spermatogenesis and sperm function. This work will provide a foundation for understanding disorders of reproductive health as well as resolving questions of male infertility and fertility regulation. [unreadable] [unreadable]